1. Field of the Invention
The present invention relates to a fluorescent display device and, more particularly, to a fluorescent display device of the matrix-display type for displaying numerals, characters, graphic forms, or the like.
2. Description of the Prior Art
Generally, the fluorescent display device for producing a visual display by bombarding the anodes coated with fluorescent material with thermions emitted from the heated filamentary cathode (hereinafter sometimes referred to as filament) has advantages in that it gives high-quality fluorescent colors, can be driven on a low voltage and is low in power consumption. Therefore, it is widely used as the display device for various electronic equipment and the like.
Heretofore, the fluorescent display device usually has a plurality of pattern display sections composed of, for instance, seven segment-shaped anodes arranged in the form of the numeral 8, and produces a visual display by the pattern display sections. Thus, it is mainly used for displaying numeric characters.
Meanwhile, with the diversification of the information to be processed by the electronic equipment and the like, it becomes necessary for the display device to display patterns in addition to numeric characters.
Accordingly, in order to display not only numeric characters but also characters and graphic forms, the fluorescent display device of the so-called matrix-display type has been developed and put into practical use, in which each pattern display section is composed of a plurality of phosphor-coated anodes in the shape of, for instance, dots arranged in the form of a matrix and in which the anodes of each pattern display section are selectively given an anode potential thereby to display characters, graphic forms, or the like.
In the case of the fluorescent display device of the matrix-display type, various modifications different in production process and drive system have been heretofore proposed. In this connection, the inventors of the present invention have already developed a fluorescent display device of the matrix-display type which can produce a visual display by the use of a reduced number of external terminals and therefore a reduced number of drive circuits.
In FIG. 1, reference numeral 1 designates a substrate made of insulating material, as glass or ceramics. On the substrate 1, there are provided wiring conductors 4, the number of which corresponds to the number of rows of phosphor-coated anodes 3 forming each of pattern display sections 2(2.sub.1 and 2.sub.2). An insulating layer 5 is laminated on the substrate 1 on which the wiring conductors 4 have been provided. The insulating layer 5 has through-holes for the respective anodes 3 to be arranged in the form of matrixes. The through-holes in insulating layer 5 are provided so that the anodes on the same row may communicate with one of the wiring conductors 4. Also, the through-holes in insulating layer 5 are filled with conductive material. The anodes 3 are provided on the through-holes filled with the conductive material so that they are electrically connected to the wiring conductors 4 through the conductive material. Column-selecting grids 6(6.sub.11 -6.sub.1m, 6.sub.21- 6.sub.2m) are provided above and opposite to the respective columns of the anodes 3 of the pattern display sections 2. Although not shown in FIG. 1, the column-selecting grids 6 positioned above and opposite to the corresponding anode columns of the respective pattern display sections 2 are electrically connected together.
Position-selecting grids 7(7.sub.1 and 7.sub.2) electrically independent of each other correspond to the respective pattern display sections 2, being provided above the column-selecting grids 6. Reference numeral 8 designates one or a plurality of filaments provided above the position-selecting grids 7 and adapted to emit thermions when heated.
In addition, a package (not shown) having at least a transparent display wall is bonded to the substrate 1 along, for instance, the periphery thereof so that the package may maintain the above-mentioned electrodes under a high vacuum. The external terminals of the electrodes are airtightly penetrated through the package.
The fluorescent display device shown in FIG. 1 may be operated as follows:
The position-selecting grids 7 provided for the respective pattern display sections 2 are successively given a positive potential with respect to the filament of filament 8 to successively select the pattern display sections 2.
While a particular pattern display section 2 is being selected by one of the position-selecting grids 7, the column-selecting grids 6 corresponding to the particular pattern display section 2 are successively given a positive potential thereby to scan the column-selecting grids 6. Simultaneously, in synchronization with the scanning of the column-selecting grids 6, the wiring conductors 4 to which the anodes 3 are connected are successively given a positive potential. As a result, thermions emitted from the filament or filaments 8 impinge on the anode 3 positioned at the point where the wiring conductor 4 given a positive potential crosses the column-selecting grid 6 given a positive potential. Thus, the layer of phosphor or fluorescent material coated on this anode 3 emits light.
In other words, when a particular postion-selecting grid 7 is being given a positive potential, the column-selecting grids 6 corresponding to the position-selecting grids 7 are scanned with the consequent result that the corresponding pattern display section 2 produces a visual display of characters, graphic forms, or the like. In this manner, the position-selecting grids 7 are scanned and thereby all the pattern display sections 2 produce a visual display of characters, graphic forms, or the like.
In this example, the number of external terminals required for giving positive potentials to the electrodes is equal to the sum of the number of the wiring conductors 4 provided according to the number of rows of the anodes 3 of each pattern display section 2, the number of the column-selecting grids 6 provided according to the number of columns of the anodes 3 of each pattern display section, the number of the position-selecting grids 7 provided according to the number of the pattern display sections 2, and the number of external terminals for the filaments 8. Therefore, the number of external terminals and that of the drive circuits can be reduced.
In this example, the wiring conductors 4 may be arranged in the arranging direction of the anodes 3. Therefore, the wiring conductors 4 are very easy to form, and its production process is greatly simplified.
As mentioned above, the fluorescent display device shown in FIG. 1 has an advantage in that its wiring conductors 4 and anodes 3 are very easy to form. However, it has a disadvantage in that the operation for arranging the position-selecting grids 7 and the column-selecting grids 6 in place is very troublesome.
More particularly, the operation for correctly arranging the column-selecting grids 6 above and opposite to the respective columns of the anodes 3 and the operation for correctly arranging the position-selecting grids 7 above the column-selecting grids 6 are both very troublesome, since they must be electrically independent of one another and must be positioned close to one another. Accurate positioning is also very difficult.
Especially, when a small-sized display device is produced or when the anodes 3 are arranged at close intervals in order to produce a fine and delicate display, the difficulties of the above-mentioned arranging operations are further intensified. In addition, in the case of the multi-row-display type fluorescent display device in which a plurality of rows of the pattern display sections 2 are provided on a single substrate 1, it is very difficult to correctly position the column-selecting grids 6 and the position-selecting grids 7 with respect to the respective pattern display sections 2, to arrange the grids 6 or 7 at a uniform height with respect to the pattern display sections 2, and to keep them in the perfectly electrically-independent condition.